CLACKAMAS, Ore. – A man carrying an AR-15 assault rifle and wearing a hockey mask made his way through the Clackamas Town Center on Tuesday afternoon shooting at customers and employees before finally turning the gun and killing himself.

Jacob Tyler Roberts, 22, would have likely shot more people but his AR-15 rifle jammed mid-way through his shooting spree, according to Clackamas County Sheriff Craig Roberts. He was, however, able to get it firing again.

WHAT INVESTIGATORS HAVE LEARNED

Jacob Roberts started his assault by driving up to the mall in his 1996 Volkswagen Jetta and then running toward the food court, Sheriff Roberts said.

From there, Roberts continued down a hallway to a lower level of the mall. He moved into a corner where he killed himself, investigators said.

At some point before shooting himself, Roberts shot and injured Kristina Shevchenko. She was able to make her way toward the REI store where she met with deputies. She was taken to OHSU and is expected to survive.

"There is no apparent relationship between the suspect and his victims," Sheriff Roberts said. Investigators do not know his motive. They added that Roberts stole the AR-15 rifle from someone he knew.

Clackamas County deputies train for active shooter scenarios. Within the last year they held a training at the Clackamas Town Center mall to practice for just this situation. The sheriff credited that training and their quick response for helping to save lives. He also thanked police departments from around the state that sent officers to help. "The level of support is absolutely amazing," Sheriff Roberts said, adding that it was remarkable there weren’t more people killed or injured. He credited four main factors:

A large number of police officers and deputies from several agencies quickly arrived at the mall. The first deputy arrived just a minute after the first call. Officers and deputies from several agencies quickly split into teams and entered the mall to find the suspect.

The suspect’s AR-15 rifle jammed during the shooting spree

The mall had a lockdown procedure in place for just this kind of incident. "They truly helped protect the lives of their customers and their employees," Sheriff Roberts said.

The 10,000 shoppers and employees in the mall kept a level head and got out of the mall in an orderly fashion. “There are just a number of heroes that took the time to help people out,” Sheriff Roberts said.

"I'd like to thank the stellar law enforcement agencies and the first responders in the area," said mall general manager Dennis Curtis. "Their response was truly amazing. They immediately took action and continue ensure the safety of everyone."

Curtis said the mall had an emergency plan in place and regularly holds emergency drills.

"In a situation like this it's either stay right where you're at or lock yourself down or go to the nearest exit and get out of the building," he said.

WHO WAS JACOB TYLER ROBERTS?

ABC News spoke with a family friend on the phone who talked on behalf of the suspect's aunt, Tami Roberts.

"Tami has no understanding or explanation for her son's behavior," she said. "We're very sorry for everyone's loss. He's always been a good boy."

The family friend said Roberts was a popular boy and everyone applauded when he got his diploma. She said the entire family is confused because Roberts "doesn't fit the profile."

The following note was give to KATU from the family:

An acquaintance of Roberts (who just wanted to go by her first name, Brittany), said she remembers the young man as jovial, popular and nice to classmates at Milwaukie High School. She said he loved skateboarding.

Jacob Roberts in a photo from his Facebook page.

She saw no indicators of any problems in high school, nor in seeing recent updates of him on Facebook.

“I am as astonished as anybody. I would have never, ever, ever thought this would happen,” she said. “As far as I knew, he was happy.”

She said Roberts was never a loner and never showed any signs of violence. She said she had a couple classes with him toward the beginning and middle of high school, but lost track of him by senior year.

"He was a popular guy. Lots of people liked him, loved him. He was really nice,” she said. “He had so many friends."

WHAT NEIGHBORS SAY

After the shooting, investigators got a warrant and searched Roberts' home off Southeast 84th Avenue in Portland. They did not say what they found inside. They also searched his car in the mall parking lot.

A neighbor near his house said Roberts was renting out the basement of a home in the 7300 block of Southeast 84th Avenue, just off Southeast Flavel.

Amber Acrey lives nearby and said she had brought mail to the house a couple of times, most recently about a week ago. Her address is the same as the suspect's address, but one street over so the mail had gotten to the wrong place.

"We just talked to him at the door," she said. "Told him 'we've got your mail, here you go.' He seemed like a nice gentleman. There didn't seem to be anything strange about him."

"He seemed normal," she added. "He seemed like an everyday person. He didn't seem like he was in distress. It didn't seem like anything was bothering him. I'm a drug and alcohol counselor so I can tell when something is bothering somebody. He didn't seem anything like that at all."

Acrey said there was nothing unusual about the mail - just your average stuff like bills.

KATU Reporter Dan Tilkin talks to resident Amber Acrey on Wednesday, Dec. 12, 2012. Acrey said she met the suspect twice, most recently in the last week, to deliver mail that had been inadvertently dropped off at her home.Photo by Shannon L. Cheesman, KATU.com Producer/Reporter.

Another local resident, Don Cross, just moved here recently from California and said he would expect something like this to happen there, but not here.

"I honestly didn't expect it," he said. "I just moved here so I don't really know that many people. I have friends that literally live on the other side of this house, so it's kind of crazy."

Cross said his first thought when the news broke about what was happening at the Clackamas Town Center on Tuesday was that it reminded him of Columbine.

"Just random acts of violence," he said. "I don't understand how someone can just do that. What's the point of it?"

Neighbor Gabriel Bell, who was with Cross when we talked to him, agreed.

"It's hard to understand," he said. "Just why more than anything."

Larry Eppler lives down the street and said he wasn't quite sure what to think about learning that the shooting suspect lived so close to him. He said the area hasn't had the best reputation but things had been getting better recently.

"We've had our share of troubles in this neighborhood," he said. "This area has long been known for drugs and prostitution but it's been getting cleaned up by getting a lot of these people moved out of here."

"It's a good place, the neighbors are good and it's extremely surprising," another nearby neighbor, David Heddy, said.

Hau Nguyen lives right next door to the suspect's home and said he was shocked to learn what was going on right outside his front door. He said he had seen the suspect a few times and given a few courteous hellos, but didn't know much else about him.